“Obesity could be driving a 50% rise in people suffering acid reflux over the last decade,” reported the Daily Mail. In acid reflux, stomach acid is regurgitated into the oesophagus, the tube that...

“Obesity could be driving a 50% rise in people suffering acid reflux over the last decade,” reported the Daily Mail. In acid reflux, stomach acid is regurgitated into the oesophagus, the tube that food passes down after it is swallowed.

The news comes from a study that found that the number of people experiencing at least one acid reflux attack a week has risen from 11.6% to 17.1% in just over a decade, while those suffering severe symptoms is up from 5.4% to 6.7%.

The large study was well-conducted, although it had some important limitations, including its reliance on people self-reporting their symptoms of acid reflux; also, much of it relied on people themselves deciding if their symptoms were minor or severe.

Most people get occasional symptoms of acid reflux, causing indigestion, or heartburn. When symptoms occur on a regular basis, the condition is called gastro-oesophageal reflux disease (GORD). While the findings are of concern, it is possible that the increase may partly be accounted for by the increasing number of older people, since the risk of GORD increases with age. The study did not look at the role of obesity, although it can increase the risk of GORD.

Where did the story come from?

The study was carried out by researchers from the Norwegian University of Science and Technology, Sweden’s Karolinska Institute and Kings College London. It was funded by a number of public institutions, including the Norwegian University of Science and Technology. It was published in the peer-reviewed medical journal, Gut.

The Mail's claim that fatty diets have triggered the increase is not proven by this research, which did not look at people’s diets. However, we do know that excess weight and obesity are on the increase and that they are a risk factor for GORD. Also the Mail's report of a 50% increase in symptoms gives the increase in relative risk (47%), which is perhaps misleading. In absolute terms, the percentage rise in people getting GORD at least once a week was 5.5% (from 11.6 to 17.1%).

What kind of research was this?

This was a population-based cohort study that examined changes in the prevalence and incidence of GORD between two periods: 1995-7 to 2006-9. Prevalence is a measure of the total number of people who have the condition at any given moment; incidence is a measure of new cases. The study also examined the number of cases of GORD that disappeared spontaneously, in other words without medication.

The researchers point out that when acid reflux occurs at least once a week it is defined as GORD. GORD is associated with a reduced health-related quality of life and an increased risk of oesophageal cancer. There are also increasing numbers of new cases of oesophageal cancer in Western countries. Yet any changes in the prevalence of GORD are uncertain.

What did the research involve?

The researchers took their data from an ongoing health study encompassing all adult residents aged 20 or over in Nord-Trondelag County, Norway. This study included giving them an assessment of GORD. This population-based study design makes the results more reliable, since by including the total population rather than say, recruiting patients from GP surgeries, it avoids any risk of selection bias.

The researchers used data from two of the study’s health surveys, the first of which took place from 1995 to 1997, and the second from 2006 to 2008. A further postal questionnaire of those who had not participated in the second survey was conducted in 2009.

In all three questionnaires participants were asked to what degree they had had heartburn or acid regurgitation during the previous 12 months and were given three response alternatives – no complaints, minor complaints or severe complaints. Those who reported minor or severe complaints were included in the category 'any GORD' while those who reported severe complaints were categorised as having severe GORD. In the third postal questionnaire, they were asked to assess the frequency of GORD – daily, weekly or less frequently.

Researchers also collected data on anti-reflux medication from the surveys and matched this against data from a national prescription database. They analysed the data using validated statistical methods, adjusting the results for sex and age.

What were the basic results?

In the first study the number of participants was 58,869 (a 64% response rate) and in the second, 44,997 (49%). Of these, 29,610 (61%) were followed up, for an average of 11 years.

Below are the main findings:

between 1995-7 and 2006-9, the number of people with at least weekly GORD increased from 11.6% to 17.1%

the number with severe symptoms increased from 5.4% to 6.7%

the number with any reflux symptoms increased from 31.4% to 40.9%

the average annual incidences of any GORD and severe GORD over this period were 3.07% and 0.23%, respectively

in women, but not men, the incidence of GORD increased with advancing age

the average annual 'spontaneous loss' (when symptoms disappear spontaneously) was 2.32% for any GORD and 1.22% for severe GORD

the chance of spontaneous loss of GORD decreased with advancing age

How did the researchers interpret the results?

The researchers suggest the increase in prevalence of GORD may be due to an increase in body weight in the population, increasing age of the cohort and possibly in women by postmenopausal hormone replacement therapy. They say the increasing numbers of people with GORD may require a 'strengthened effort' to investigate and treat the condition.

Conclusion

This was a well-conducted study and its size reduces the risk of findings being due to chance. While it does suggest that the incidence of GORD may be rising, it does have some important limitations:

It relied on people self-reporting their symptoms of acid reflux and also recalling how often symptoms had occurred over the last 12 months, rather than, for example, using medical records. Relying on self-reporting, particularly when people have to remember symptoms over a period of months, can make the results less accurate.

The first two surveys used did not ask people specifically how many attacks of reflux they had, although the researchers say they conducted a smaller study to validate the results.

There was a sharp drop in participants between the two surveys, which introduces the risk of selection bias: it could be the case that those people who had GORD were more likely to participate in the second phase, while people without the condition had no interest in continuing the study. This could skew the results and suggest higher rates of GORD.

The rise in prevalence could partly be due to the rise in age of the participants, although the researchers say they adjusted their results for age.

In conclusion, the possible increase in GORD and its causes requires further investigation.